This invention relates to optical communications systems and, in particular, to an integrated dual-wavelength transceiver for such systems.
Due to their low-cost and high bandwidth characteristics, optical fibers are utilized in a wide variety of communication systems. Such utilization has been particularly valuable in long-haul systems where the cost of expensive equipment is shared by thousands of individual customers.
Considerable development effort has been directed to devising economical optical fiber systems capable of delivering broadband signals (for example, voice, data and video) directly to customer premises. One such approach involves running optical fiber from a central office to each customer location and providing an optical network unit between the fiber and the customer. An incoming dual wavelength signal, typically 1.3 and 1.5 micrometer wavelengths, can be constantly applied from a central office to each network unit. In each unit, the incoming signal is split into the two wavelength portions. One portion is detected and then applied as an electrical signal to the customer equipment. Another portion is modulated with electrical signals from the customer and then sent back as an optical signal to the central office. An integrated network unit for performing this function is described in applicants U.S. Pat. No. 5,577,138 issued Nov. 19, 1996.
It has more recently become apparent that with increasing demand for bandwidth, in customer originated signals, it would be desirable to provide network units with their own sources of light instead of requiring a constant optical carrier from the central office. However, units providing light sources are conventionally constructed of discrete components, are relatively bulky, and are expensive for large scale deployment. Accordingly there is a need for such a transceiver unit that can be integrated at an economical cost for providing broadband service to individual customers.
In accordance with the invention, an integrated dual wavelength transceiver comprises a multilayer monolithic structure that functions as an optical waveguide, a photodetector, and a light emitter. In an alternative embodiment, second spaced apart portion on the same substrate can provide an amplifier to amplify electrical signals generated by the photodetector.